The hard bremsstrahlung correction to $e^+ e^- \to 4f$ with finite fermion masses: results for $e^+ e^- \to u \bard} \mu^- \bar{\nu}_{\mu}$

Abstract.

An improved efficient method of calculating the hard bremsstrahlung correction to $e^+ e^- \to 4f$ for non-zero fermion masses is presented. The non-vanishing fermion masses allow us to perform the phase space integrations to the very collinear limit. We therefore can calculate cross sections independent of angular cuts. Such calculations are important for background studies. Results are presented for the total and some differential cross sections for $e^+ e^- \to u \bar{d} \mu^- \bar{\nu}_{\mu}$ and the corresponding hard bremsstrahlung process. The latter is of particular interest for a detailed investigation of the effects of final state radiation. In principle, the process $e^+ e^- \to u \bar{d} \mu^- \bar{\nu}_{\mu}\gamma$ is also interesting since it helps to set bounds on possible anomalous triple and quartic gauge boson couplings involving photons. The size of mass effects is illustrated by comparing the final states $u \bar{d} \mu^- \bar{\nu}_{\mu}(\gamma)$, \(c \bar{s} \mu^- \bar{\nu}_{\mu}(\gamma)$ and $u \bar{d} \tau^- \bar{\nu}_{\tau}(\gamma)\).